The present invention relates to a distance measurement system and more particularly but not exclusively to determining a distance between the core of a resonant circuit and a ferromagnetic or paramagnetic element.
Mechanical fixtures such as joints and bearings often suffer from performance degradation due to material wear. When the wear becomes pronounced this may result in loss of efficiency or damage to the system in which it is installed. This wear may be difficult to measure, as it generally involves small displacement changes and develops slowly over time. Additionally, the fixtures may be in inaccessible locations. Thus, in order to detect such wear, a sensor is needed which can detect small changes in the distance between two interior locations.
Koeplin, et al. in U.S. Pat. No. 4,914,951 describes an ultrasonic sensor for measuring the distance from a transducer to an object. These sensors have particular applicability for motor vehicles. The invention uses at least one electroacoustic transducer to transmit an ultrasonic signal and to receive the ultrasonic signal reflected by an object. An electric generator is used to activate the transducer. A receiving stage is provided for the echo signals picked up by the transducer. A control unit uses the generator to activate the transducer for a predetermined transmission time. The transducer then decays for a time following its activation to provide a reception window for receiving the reflected echo signals. Ultrasonic signals are not always suitable for detecting material wear.
According to a first aspect of the present invention there is thus provided a distance measurement system, comprising at least one resonant circuit, at least one magnetic element with predetermined magnetic properties, a transmitter operable to transmit an electromagnetic pulse, a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and an analyzer operable to analyze an amplitude envelope property of the oscillations, to thereby determine a distance between the resonant circuit and the magnetic element. In an embodiment, the magnetic element is ferromagnetic. In another embodiment the magnetic element is paramagnetic. In an additional embodiment, the analyzer is operable to determine the amplitude envelope property from an absolute value of amplitudes of the oscillations. In another embodiment the analyzer is operable to determine the amplitude envelope property from relative amplitude values of more than one cycle of the oscillations. In an embodiment the amplitude envelope property is an amplitude rate of decay. In an additional embodiment the analyzer is operable to determine the distance between the resonant circuit and the magnetic element additionally from frequency properties of the oscillations.
In a preferred embodiment the distance measurement system comprises more than one resonant circuit, to thereby determine more than one distance between the resonant circuits and the at least one magnetic element. Another embodiment is operable to determine the distance between the resonant circuits and the at least one magnetic element in more than one dimension. In another embodiment the more than one resonant circuits are operable to resonate at different frequencies.
Another embodiment comprises more than one magnetic element, to thereby determine more than one distance between the at least one resonant circuit and the magnetic elements. Another embodiment preferably is operable to determine the distance between the at least one resonant circuit and the magnetic elements in more than one dimension.
Another embodiment comprises more than one resonant circuit and more than one magnetic element, to thereby determine more than one distance between the resonant circuits and the magnetic elements. Another embodiment preferably is operable to determine the distance between the resonant circuits and the at least one magnetic element in more than one dimension.
In a preferred embodiment the analyzer comprises a look-up table, comprising relationships between measured oscillations and distances. In another embodiment the relationships are per-system relationships. In an additional embodiment, the relationships comprise in-situ calibrations.
According to a second aspect of the present invention there is thus provided a method for assembling a distance measurement system, comprising the steps of: placing a resonant circuit at a first location, placing a magnetic element with predetermined magnetic properties at a second location, providing a transmitter for transmitting an electromagnetic pulse to the resonant circuit, providing a detector for detecting oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and providing an analyzer for analyzing an amplitude envelope property of the detected oscillations, to thereby determine a distance between the first location and the second location. In an embodiment, the analyzer comprises a look-up table of relationships between measured oscillations and distances, and wherein the look-up table values are established for each one of a predetermined set of distances by performing for each predetermined distance the steps of: transmitting an electromagnetic pulse to the resonant circuit, detecting oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and measuring an amplitude envelope property of the detected oscillations, to thereby establish a look-up table value for the distance.
According to a third aspect of the present invention there is thus provided a method for measuring the distance between a first location comprising a resonant circuit and a second location comprising a magnetic element, comprising the steps of: transmitting an electromagnetic pulse to the resonant circuit, detecting oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and analyzing an amplitude envelope property of the detected oscillations, to thereby determine a distance between the first location and the second location. In a preferred embodiment, the step of analyzing an amplitude envelope property further comprises comparing information detected from the emitted oscillations to information in a look-up table, of relationships between measured oscillations and distances. Another embodiment comprises obtaining the amplitude envelope property from an absolute value of amplitudes of the oscillations. Another preferred embodiment comprises obtaining the amplitude envelope property from relative amplitude values of more than one cycle of the oscillations. Another embodiment, comprises making use of an amplitude rate of decay as the amplitude envelope property. Another embodiment comprises additionally detecting the distance from frequency properties of the detected oscillations.
According to a fourth aspect of the present invention there is thus provided a distance measurement system utilizing eddy currents for energy dissipation, the system comprising: at least one resonant circuit, at least one magnetic element with predetermined magnetic properties, a transmitter operable to transmit an electromagnetic pulse, a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and an analyzer operable to analyze an amplitude envelope property of the oscillations as an indicator of eddy current induced energy dissipation, to thereby determine a distance between the resonant circuit and the magnetic element.